1. Field of the Invention
The present invention relates generally to the control of a hybrid electric vehicle, and more particularly to a method for controlling charging of a power source of a hybrid electric vehicle.
2. Background Art
Hybrid electric vehicles employ a plurality of power sources that provide power to drive vehicle traction wheels and support electrical loads. In the case of a power source that stores energy, such as a battery, it is desirable to maintain a nominal or full state of charge to adequately support electrical loads and provide “boost” to the vehicle drivetrain to support acceleration requests.
If an energy-storing power source becomes depleted, it may be recharged using another power source, such as an engine. Recharging with such a power source reduces the torque available to propel the vehicle. If more wheel torque is needed to accommodate changes in driver demand or road load conditions, then the charging torque must be removed in a way that is imperceptible to the driver, yet provides the desired vehicle performance.
Applicants' of the present invention have discovered that the sensitivity of an accelerator pedal or similar input device may be affected as a power source approaches a full state of charge. More specifically, less torque is utilized to charge a power source as it nears or reaches a full state of charge. Thus, more torque is available to propel the vehicle. As more propulsion torque becomes available, accelerator pedal actuation may produce more torque than expected by the vehicle operator. Consequently, the “feel” of level of responsiveness of the accelerator pedal may change as the power source nears a full state of charge.
Before Applicants' invention, there was a need for an improved method of charging one or more power sources of a hybrid electric vehicle. In addition, there was a need to provide a smooth transition out of a power source charging mode that is not perceived by a vehicle operator and does not degrade vehicle performance. In addition, there was a need to provide a consistent feel or level of responsiveness of an accelerator pedal that is not affected by power source charging. Problems associated with the prior art as noted above and other problems are addressed by the Applicants' invention as summarized below.